The quantitative determination of analytes in body fluids is of great importance in the diagnoses and maintenance of certain physiological abnormalities. For example, lactate, cholesterol and bilirubin should be monitored in certain individuals. In particular, it is important that diabetic individuals frequently check the glucose level in their body fluids to regulate the glucose intake in their diets. The results of such tests can be used to determine what, if any, insulin or other medication needs to be administered. In one type of blood-glucose testing system, sensors are used to test a sample of blood.
A test sensor contains biosensing or reagent material that reacts with blood glucose. The testing end of the sensor is adapted to be placed into the fluid being tested, for example, blood that has accumulated on a person's finger after the finger has been pricked. The fluid is drawn into a capillary channel that extends in the sensor from the testing end to the reagent material by capillary action so that a sufficient amount of fluid to be tested is drawn into the sensor. The fluid then chemically reacts with the reagent material in the sensor resulting in an electrical signal indicative of the glucose level in the fluid being tested. This signal is supplied to the meter via contact areas located near the rear or contact end of the sensor and becomes the measured output.
Diagnostic systems, such as blood-glucose testing systems, typically calculate the actual glucose value based on a measured output and the known reactivity of the reagent-sensing element (test-sensor) used to perform the test. The reactivity or lot calibration information of the test sensor may be given to the user in several forms including a number or character that they enter into the instrument. One prior art method included using an element that is similar to a test sensor, but which was capable of being recognized as a calibration element by the instrument. The test element's information is read by the instrument or a memory element that is plugged into the instrument's microprocessor board for directly reading the test element.
These methods suffer from the disadvantage of relying on the user to enter the calibration information, which some users may not do. In this event, the test sensor may use the wrong calibration information and thus return an erroneous result. Improved systems use an auto-calibration circuit or label that is associated with the sensor package. The auto-calibration circuit or label is read automatically when the sensor package is placed in the meter and requires no user intervention.
The success of sensing instruments has lead to the development of improved sensing instruments and improved sensors. For example, existing sensing instruments analyze the sample for a predetermined length of time equal to approximately 30 seconds. New improved sensing instruments, however, are designed for much shorter analysis times (e.g., 5 seconds) and the calibration information for the test sensor measured at the 30 seconds analysis time is likely to be different from the calibration information relevant to shorter analysis time.
As new and improved instruments or meters are being developed and used by consumers, the older instruments or meters will still be used for an unknown period of time. If calibration codes adapted for characteristics of the new and improved instruments are used in older meters, test results may be inaccurate, which is undesirable. It would be desirable to provide a device and method that provides the lot calibration information of the test sensor to at least two instruments or meters in a reliable manner. It would also be desirable for this device to be as compact as possible as the label has to fit into the restricted space available on the sensor package.